Projection system, in particular for three dimensional representations on a viewing device

ABSTRACT

The present invention relates to a projection system especially intended for projecting three-dimensional representations on a viewing device ( 8, 12 ), where the representations submitted to the watcher&#39;s eye are put in relation with the respective point where the watcher stands ( 6,7 ), to whom sensors are allocated for locating his or her relative position, so that he or she sees on the viewing device an image virtually represented in space in relation to his or her position. In order to allow for the various three-dimensional representations to be viewed by many watchers on the same viewing device, the system projects several image representations simultaneously, each corresponding to the watcher&#39;s relative position. Each watcher is allocated image separating apparatus which enable his or her access to image representations corresponding to the place where he or she stands. With the inventive system a projection of virtual objects is obtained which is close to a holographic representation, including in a stereoscopic representation.

The invention has to do with a system for projecting pictorialrepresentations, in particular 3D images, onto a viewing device inaccordance with the general description given in claim 1.

Three-dimensional objects are frequently represented on a viewing deviceas two-dimensional images, for which the viewing angle and position ofthe viewer relative to the stationary projection screen determine theaspect of the object presented by the image at a particular time. Thisrequires that the location of the viewer relative to the screen beascertained in spatial coordinates by appropriate sensors, and that therepresentation on the screen be suitably calculated and adjusted by anappropriate tracking system. When such a procedure is employed, and whena single projection screen is used, only one viewer at a time can see arepresentation of the object on the screen corresponding to thatviewer's position; other viewers see a distorted image.

With a different procedure for viewing an object that is virtuallystationary in space, one projection screen is assigned to a particularviewer, and remains so assigned for the duration of the viewing. Theposition of the viewer at any given time is registered by the trackingsystem, and anytime the viewer's position changes, the representation ofthe object is calculated and displayed afresh in real time as a functionof the location and the viewing angle of the viewer. Such a systemgenerally employs a helmet having viewing devices which are placed indirect relationship with the viewer's eyes, e.g., a LCD screen. However,such helmets are unwieldy and moreover can be used only by a singleviewer. Furthermore, the viewer's natural environment cannot easily beincluded in the representation provided by such a helmet. When this kindof procedure is employed, though, the tracking system can also analyzethe screen's position and the direction in which the screen ispresenting the image, making a helmet unnecessary. There is still only asingle representation on the screen, however.

A true stereoscopic projection makes possible more detailed views ofspatial relationships. For example, forms and shaped parts, or workingparts, can be represented in detail with lights and shadows. When it isa matter of a real-time representation that is derived from a computer,the visual appearance of the object can be directly modified.

To achieve a true stereoscopic representation of an image by projectiononto a canvas projection screen or by display on a video projectionscreen, in the main two procedures are used that require employment ofspectacles whose lenses function as image separators and which make itpossible to make different image data available to the right eye and tothe left eye.

In the case of the passive procedure, the lenses of the spectacles arepolarized differently; for example, at an angle of 90° to each other orcircularly in opposite directions. The image shown on the canvasprojection screen must be polarized in a corresponding fashion. This canbe achieved, for example, by using projectors having polarizationorientations that are different for the right and the leftrepresentation of the object.

For the active procedure, no polarization filters are required. Instead,the separation of the images is effected by means of sequentialrepresentation of the image data assigned to the left and the right eye.Through a synchronous tracking system, LC spectacles (shutter-lensspectacles) are switched over in the same rhythm so that the viewer canperceive with each eye only the image information assigned to that eye.The clock-pulse frequency of the switching determines the degree towhich the viewer sees a flickering.

With regard to both the passive and the active forms of this technique,one or several persons can apprehend at the same time only the sameinformation. If, for example, stereoscopic representations of workroutines and operations are wanted, in order to convey to the viewer astereoscopic image of a certain phase space coordinated with theviewer's physical location, and if it is also desired that the phasespace coordinated with a second person's position be shown to thissecond person, and if the two images of the phase space are different,then it is undesirable that the same 3D image be shown to both viewers.

A representation of an object corresponding to its natural appearance,and one that allows several viewers to perceive different aspects of theobject, can be achieved at the present time only with a holographicrepresentation. A real-time representation of objects of considerablesize, e.g., of an automobile, that permits modification of the object,is not yet possible, however, and does not appear to be even conceivablein the foreseeable future.

A system for displaying two different images in the form of 2Drepresentations on a single viewing device is known from U.S. Pat. No.4,879,603. The displays for separate viewers are separated from oneanother by image-separating devices consisting of circular polarizers.The resulting image is not a stereoscopic one.

EP-A-O 656 555 presents a projection system for 3D representations thatenables a viewer to see a 3D image. In this system, two projectionscreens are used which effect a right/left separation by means of asystem of mirrors. These two 3D images are separated in a manner takinginto account the viewer's position. This is done by usingextraordinarily complicated lighting devices or lenticular assemblies.Each stereoscopic image is coordinated with just one single position(which can be changed only slightly), which can be occupied by only asingle viewer at a time.

The invention is intended to provide a system for projectingnon-holographic 3D representations, in particular stereoscopic images,onto a viewing device, with the aid of which system the simultaneousrepresentation of different image contents, approximating a holographicrepresentation, for several viewers is possible,

This purpose is fulfilled by the invention described in claim 1.Modified forms of the invention offering advantages are described insub-claims.

The invention consists of a system for projecting non-holographic 3Dimages onto a viewing device. In this system, the images assigned to theviewer's eyes are brought into relationship with the viewer's positionat a particular time by sensors which are assigned to the viewer, andwhich ascertain the viewer's position at a given time, and by thedisplay on the viewing device of an object whose virtual spatialpositioning corresponds to the viewer's standpoint. For the purpose ofsimultaneous perception of different 3D images on the same viewingdevice by several viewers, several different images that are coordinatedwith the various locations of the viewers are displayed simultaneously.Image-separating devices are assigned to the several viewers, by meansof which each viewer has access only to the images that are coordinatedwith that particular viewer's position. For stereoscopic viewing of theobject, two 3D images, which are separated by image separators andassigned to a viewer's right and left eyes, are provided to each viewer.

With the aid of the system in question, it is possible for a number ofviewers to view an object on the viewing device from different positionssimultaneously, with the viewing angle of each person corresponding tothe actual viewing angle of the virtually stationary object. It istherefore possible for one person to view a certain aspect of theobject, while at the same time another person is seeing a differentdetail of the object.

The images assigned to the several viewers can be displayed sequentiallyin time. The image-separating devices are in that case shutter-lensspectacles that are synchronized with the images; the shutter lenses ofa particular viewer allow passage of the projected light only when theimage assigned to that particular viewer is displayed.

In an alternate embodiment of the invention, the images assigned to theseveral viewers are displayed simultaneously, but are polarizeddifferently on the projection screens. In this case, theimage-separating devices are spectacles with polarization lenses whichpermit passage only of the images corresponding to their polarizationorientation and to the particular viewer's standpoint.

To accomplish a stereoscopic projection, images that are separated byimage separators are supplied as assigned to the left and the right eyesof the viewers.

If shutter-lens spectacles are used for the stereoscopic projection, itis preferable that the length of time during which the pertinent shutterlenses of a viewer are switched to allow passage of light for each eyewithin a period of the clock-pulse frequency, be shortened in proportionto the number of viewers, or that the clock-pulse frequency of therepresentation be increased in proportion to the number of viewers, sothat the flickering does not become stronger due to the intervals of thetemporal sequence in which the representation occurs.

If the system of projection of stereoscopic 3D images is employed fortwo viewers, they are then able to perceive the image data assigned [toeach of them] simultaneously, but each perceives only the data assignedto him. This makes it possible, for example, to visualize productionoperations that are carried out jointly considerably better than ispossible when it is a matter of an image produced by a singlestereoscopic projection.

The system provided for by the invention can be employed veryadvantageously for the projection or representation of 3D-image data ona computer-controlled screen or for a projection device that iscontrolled by computers.

A single projection device can be used that projects the differentimages successively. Alternatively, a system can be used in which aseparate projection device is assigned to each viewer. When the systemprovided for by the invention is used with two viewers and withstereoscopic projection, four alternative image sequences can beemployed. The selection of the particular sequence depends on whichparticular image is to be shown, inasmuch as the crosstalk between thedifferent channels must be taken into account, as well as on which kindof shutter lenses are being used and which kind of projection technologyis being applied.

In a preferred embodiment of the invention, the means of separating theright- and the left-eye information for the individual viewers arepolarization orientations, and the means used to separate the imagesviewed among the various viewers are shutter configurations. Theassignment [of these means] can also be the reverse.

Linearly or circularly polarized filters on appropriately equippedprojectors, for example, can be used as polarization devices. Then thefirst viewer or the first group of viewers is given shutter lenses withthe first polarization orientation, and the second viewer of group ofviewers is given shutter lenses with the second polarizationorientation. Possible loss of light due to the polarization filters canbe compensated for by using several projectors for each individualviewer or each group of viewers.

It is preferable that the projection surface be a cylindrical screenwithin which the object to be viewed is virtually situated in a stablemanner. Should from-above or from-below information be desired, there isa further-developed embodiment of the invention employing a sphericallyshaped projection surface within which the object is virtually fixed inplace. In both cases, the projection screens are illuminated fromwithin. Thus a viewer located outside of the projection assemblyexperiences the illusion that the object being viewed is situated withinthe space enclosed by the projection surface. In the case of astereoscopic projection, the object can therefore be seen asintersecting the projection surface, depending on the adjustment of thestereoscopic apparent window.

The system provided for by the invention allows the viewing of objects,even those of considerable size, in the manner of a holographicrepresentation. The represented objects can be the photographicallyrealistic representations of an object; they can, however, also becomputer-generated graphics, the shape of which can be alteredinteractively. Applications of this kind can be used especially in theconstruction and design of machine parts, automobile parts, and otherproducts. When a cylindrical or spherical projection surface isemployed, the viewers can move around the object in a circular path.Alternatively, the same effect can be achieved by virtually rotating theobject while the viewer remains stationary. In this case no trackingsystem is necessary.

When a cylindrical or spherical projection surface is used, therepresented object can be displayed seamlessly and in a homogeneousfashion. To achieve such a display, well-established image-processingprocedures used to improve edges can be employed to avoid, for example,the appearance of edges on adjacent images.

The invention is explained in more detail below using an exemplaryembodiment of it. The figures show the following:

FIG. 1 a general view of a projection device with which shutter-lensspectacles are used,

FIGS. 2a-d a listing of different display sequences for two viewers,

FIG. 3 a cylindrical projection device containing the representation ofa virtual object, and

FIG. 4 a spherical projection device with a virtual object representedin its interior.

FIG. 1 shows a computer 1 which is connected with a projector 5 and/or amonitor 4 and transmits video signals to them. The computer also sends acontrol signal to an infra-red transmitter 2 which sends infra-redsignals to the receiver that is located in the shutter-lens spectacles3. The computer 1 is gated in such a way that images are displayedsequentially on the monitor 4 or the projection device 5; these imagescan be viewed with the shutter-lens spectacles 3 which are switched overin the appropriate rhythm by the infra-red gating so that a stereoscopicimage appears for the viewer.

The fundamental principle of the gating of the displays by means ofprojectors 5 or monitors 4 and of the switching of the shutter-lensspectacles 3 is the same whether there is one or several viewers. When asingle image is shown for several viewers, a correspondingly increasednumber of shutter-lens spectacles is used. When the device shown in FIG.1 is employed for the simultaneous display of different stereoscopicimages for a number of viewers, the computer 1 must be gated in such amanner that the sequence of the different images is correctlytransmitted to the viewers to which they are assigned.

FIG. 2 shows four alternative possibilities of the sequentialstereoscopic display of different images for two viewers. Theabbreviations appearing in the left column mean: 1L=left eye of viewer1; 1R=right eye of viewer 1; 2L=left eye of viewer 2; 2R=right eye ofviewer 2.

FIG. 2a shows the display sequence 1L, 1R, 2L, 2R, which is repeated inevery period of the clock-pulse frequency. FIG. 2b shows the sequence1L, 2L, 1R, 2R. FIG. 2c shows the sequence 1L, 1R, 2R, 2L, while FIG. 2dshows the sequence 1L, 2R, 1R, 2L. The image sequences of FIGS. 2b and dhave the advantage that, on the one hand, the viewer's subjectiveperception of flickering is reduced, since in these sequences the imagessucceed one another temporally in a more regular manner in comparison tothe sequences of FIGS. 2a and c, and, on the other hand, the crosstalkbetween the left and the right image is considerably reduced owing tothe temporal interval [between them]. When, in addition, the images forthe first and the second viewer differ only slightly, then the crosstalkbetween the viewers' images is also relatively slight.

Although flickering is heightened by the procedure provided for by theinvention when it is a matter of a stereoscopic representation, incomparison to a single image, this effect can be diminished byincreasing the clock-pulse frequency of the display, for example to160-180 Hz. The limit to which that frequency can be increased isdetermined solely by the maximum switching rate of the shutter-lensspectacles.

To double the number of viewers and of the simultaneous images, theshutter-lens spectacles and the projection devices can additionally beprovided with polarization filters that are either polarized linearly indifferent directions or circularly polarized. The light attenuationoccurring because polarization filters are used can be compensated forby increasing the projectors' light intensity, by employing severalprojectors for each viewer and/or each polarization orientation, or evenby using many projectors for each individual image of a single eye[assigned to a single eye?].

Although the discussion of this exemplary embodiment treats of only twoor four viewers, the number of viewers who view the same image at aparticular time is, of course, not limited to two or four, but may be asmany as desired.

FIG. 3 shows a projection assembly which includes a cylindrical videoscreen 8 which is equipped with a suitable panoramic projection devicein its interior. Two viewers 6 and 7 are located outside the projectionscreen. The projector or the projectors cast a virtual image from theassembly's interior onto the projection surface. The figure shows thevirtual image 9 of an automobile. For two viewers, two representationsare required which can be separated from one another by means ofappropriate polarization filters or by shutter configurations. When apolarization device is used, the first projector casts an image in thefirst polarization orientation onto the projection screen, while thesecond projector is equipped with a second polarization device whichprovides, preferably, a polarization orientation that is perpendicularto the first polarization orientation. If the two viewers are wearingappropriate polarization-lens spectacles, the images cast onto thecylindrical screen by the projectors can be made available to theviewers separately. Thus, at a given time, the two viewers 6 and 8 seeonly the image assigned to them. For example, the viewer 8 sees detail10, whereas the viewer 7 sees detail 11 of the virtual image 9.

Unless additional measures are taken, the viewers are only able toperceive two different images. However, if a tracking system of thefamiliar kind is used, the images can be calculated and tracked by meansof a computer in such a way that when the viewers 6 and 7 move in acircle around the cylindrical projection screen, the images arecontinually calculated afresh, so that the object 9 appears as virtuallystationary, while the viewer moves around the projection screen. Theviewer then experiences the illusion that he is able to regard theobject from all sides. If a sufficiently fast computer is employed tocontinually provide newly calculated images that are a function of theviewer's standpoint at any given time, the virtual object appears to theviewer as a real object that can be regarded from different sides.

FIG. 4 shows a spherical projection assembly 12 that also makes itpossible to view the virtual image 9 within the interior of theprojection surface. In the case of this kind of projection assembly, inaddition to the kind of image provided by the projection assembly shownin FIG. 3, a view from above and from below is also possible, so thatthe virtual object can be apprehended in the totality of its aspects.

The illusion of a virtual object is significantly enhanced if thevirtual image is displayed as a stereoscopic representation. The viewersmust then wear image separators in order to be able to coordinate witheach of the viewer's eyes the stereoscopic image assigned to thatparticular eye. The image separators are either shutter-lensconfigurations or polarization devices. The result is that the imagedoes not appear to the viewers as only displayed on a flat surface, butinstead appears virtually in space. It is possible to define thestereoscopic perspective through appropriate adjustment of theindividual images in such a fashion that the objects being viewed appearto the viewers as detached from the plane of the projection surface. Avisual experience is thereby produced that approximates a holographicrepresentation.

With the aid of the procedure provided for by the invention it is thuspossible to provide completely different 3D images on a canvasprojection screen or a video screen for two or more viewers. This isvery advantageous especially for visual representations of workoperations for instructional purposes.

What is claimed is:
 1. A system for projecting non-holographic 3D imagesof an object onto a 2D viewing device and which permits a plurality ofviewers to simultaneously view different aspects of the object displayedon the viewing device in accordance with their respective position fromthe viewing device, the system comprising: a viewing device; sensormeans assigned to each viewer for ascertaining the assigned viewerposition relative to said viewing device; a display source fordisplaying a plurality of different 3D images simultaneously onto saidviewing device for the purpose of simultaneous perception by eachviewer; means responsive to said sensor means for coordinating thesimultaneously displayed images with each viewer's position at any giventime; and image-separating means for separating said plurality ofdisplayed 3D images into respective viewer assigned images that areviewable only by an assigned viewer in accordance with their position,and wherein different pictorial representations are displayed by asingle projection device which projects the representationssequentially.
 2. A system in accordance with claim 1, wherein saidviewing device is selected from the display group consisting of acathode-ray tube and an LC display.
 3. A system for projectingnon-holographic 3D images of an object onto a 2D viewing device andwhich permits a plurality of viewers to simultaneously view differentaspects of the object displayed on the viewing device in accordance withtheir respective position from the viewing device, the systemcomprising: a viewing device; sensor means assigned to each viewer foras certaining the assigned viewer position relative to said viewingdevice; a display source for displaying a plurality of different 3Dimages simultaneously onto said viewing device for the purpose ofsimultaneous perception by each viewer; means responsive to said sensormeans for coordinating the simultaneously displayed images with eachviewer's position at any given time; image-separating means forseparating said plurality of displayed 3D images into respective viewerassigned images that are viewable only by an assigned viewer inaccordance with their position, wherein: said plurality of 3D images aredisplayed sequentially; and said image-separating means compriseshutter-lens spectacles having lenses synchronized with said pluralityof 3D images.
 4. A system in accordance with claim 3, wherein: saidplurality of 3D images include left and right eye images forstereoscopic viewing of the object; and said system further includesimage separators for separating the left and right eye images for eachviewer.
 5. A system in accordance with claim 3, wherein a length of timein which the shutter-lens spectacles are switched is shortened inproportion to the number of viewers to minimize image flickering.
 6. Asystem in accordance with claim 5, wherein a clock pulse frequency of animage is increased in proportion to the number of viewers using thesystem.
 7. A system in accordance with claim 5, wherein an object isbeing represented for two viewers and a pictorial representation of saidobject takes place in one of the following sequences: a) left eye viewer1 right eye viewer 1 left eye viewer 2 right eye viewer 2 b) left eyeviewer 1 left eye viewer 2 right eye viewer 1 right eye viewer 2 c) lefteye viewer 1 right eye viewer 1 right eye viewer 2 left eye viewer 2 d)left eye viewer 1 right eye viewer 2 right eye viewer 1 left eye viewer2.


8. A system in accordance with claim 6, wherein an object is beingrepresented for two viewers and a pictorial representation of saidobject takes place in one of the following sequences: a) left eye viewer1 right eye viewer 1 left eye viewer 2 right eye viewer 2 b) left eyeviewer 1 left eye viewer 2 right eye viewer 1 right eye viewer 2 c) lefteye viewer 1 right eye viewer 1 right eye viewer 2 left eye viewer 2 d)left eye viewer 1 right eye viewer 2 right eye viewer 1 left eye viewer2.


9. A system in accordance with claim 4, wherein: said image separatorscomprise polarization configurations; and said image-separating meanscomprise shutter-lens configurations.
 10. A system in accordance withclaim 4, wherein said image separators comprise shutter-lensconfigurations; and said image-separating means comprise polarizationconfigurations.
 11. A system in accordance with claim 3, wherein saidviewing device is selected from the display group consisting of acathode-ray tube and an LC display.
 12. A system for projectingnon-holographic 3D images of an object onto a 2D viewing device andwhich permits a plurality of viewers to simultaneously view differentaspects of the object displayed on the viewing device in accordance withtheir respective position from the viewing device, the systemcomprising: a viewing device; sensor means assigned to each viewer foras certaining the assigned viewer position relative to said viewingdevice; a display source for displaying a plurality of different 3Dimages simultaneously onto said viewing device for the purpose ofsimultaneous perception by each viewer; means responsive to said sensormeans for coordinating the simultaneously displayed images with eachviewer's position at any given time; image-separating means forseparating said plurality of displayed 3D images into respective viewerassigned images that are viewable only by an assigned viewer inaccordance with their position; and wherein said image-separating meanscomprise polarization lenses which permit passage of the 3D imagescorresponding to polarization orientation and viewpoint of a particularviewer.
 13. A system in accordance with claim 12, wherein said viewingdevice is a projection screen.
 14. A system in accordance with claim 12,wherein said viewing device includes a cylindrical projection screen andimages are projected onto a surface of said cylindrical projectionscreen from inside said cylindrical projection screen.
 15. A system inaccordance with claim 12, wherein said viewing device includes aspherical projection screen and images are projected onto a surface ofsaid spherical projection screen from inside said spherical projectionscreen.
 16. A system in accordance with claim 13, wherein differentpictorial representations are displayed by a single projection devicewhich projects the representations sequentially.
 17. A system inaccordance with claim 14, wherein different pictorial representationsare displayed by a single projection device which projects therepresentations sequentially.
 18. A system in accordance with claim 15,wherein different pictorial representations are displayed by a singleprojection device which projects the representations sequentially.
 19. Asystem in accordance with claim 13, wherein a projection device isassigned to each polarization orientation of said shutter-lensspectacles.
 20. A system in accordance with claim 14, wherein aprojection device is assigned to each polarization orientation of saidshutter-lens spectacles.
 21. A system in accordance with claim 15,wherein a projection device is assigned to each polarization orientationof said shutter-lens spectacles.
 22. A system in accordance with claim12, wherein: said plurality of 3D images include left and right eyeimages for stereoscopic viewing of the object; and said system furtherincludes image separators for separating the left and right eye imagesfor each viewer.
 23. A system in accordance with claim 22, wherein: saidimage separators comprise polarization configurations; and saidimage-separating means comprise shutter-lens configurations.
 24. Asystem in accordance with claim 22, wherein said image separatorscomprise shutter-lens configurations; and said image-separating meanscomprise polarization configurations.